U.S. patent number 10,429,246 [Application Number 15/792,459] was granted by the patent office on 2019-10-01 for panoramic reconstruction of temporal imaging.
This patent grant is currently assigned to The University of Hong Kong. The grantee listed for this patent is The University of Hong Kong. Invention is credited to Bowen Li, Kenneth Kin Yip Wong.
United States Patent |
10,429,246 |
Wong , et al. |
October 1, 2019 |
Panoramic reconstruction of temporal imaging
Abstract
The panoramic-reconstruction temporal imaging (PARTI) system is
a single-shot optical waveform measurement apparatus that achieves
scalable record length and sub-picosecond resolution simultaneously
for ultrafast non-repetitive waveform characterization, in analogy
with the wisdom of stitching multiple mosaic images to achieve
larger-field-of-view in the spatial domain. It consists of a
high-fidelity optical buffer, a low-aberration time magnifier and
synchronization-control electronics. For specific measurement
circumstances, the PARTI system can also be carried out based on a
passive optical buffer, which reduces the system complexity. The
PARTI system is configured for real-time single-shot
characterization of non-repetitive optical dynamic waveform that
evolves over a time scale much larger than that of its ultrafast
temporal details, i.e., optical dynamics with large time-bandwidth
product.
Inventors: |
Wong; Kenneth Kin Yip
(Pokfulam, HK), Li; Bowen (Kennedy Town,
HK) |
Applicant: |
Name |
City |
State |
Country |
Type |
The University of Hong Kong |
Hong Kong |
N/A |
CN |
|
|
Assignee: |
The University of Hong Kong
(Hong Kong, CN)
|
Family
ID: |
66169860 |
Appl.
No.: |
15/792,459 |
Filed: |
October 24, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190120696 A1 |
Apr 25, 2019 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01J
11/00 (20130101); G01J 9/00 (20130101); H01S
3/06791 (20130101); H01S 3/1003 (20130101); H01S
3/06754 (20130101); G02B 6/2861 (20130101) |
Current International
Class: |
G01J
11/00 (20060101); G02B 6/28 (20060101); H01S
3/067 (20060101); G01J 9/00 (20060101) |
Other References
Li, Bowen, et al. "Panoramic-reconstruction temporal imaging for
seamless measurements of slowly-evolved femtosecond pulse
dynamics." Nature communications 8.1 (Jul. 5, 2017): 61. (Year:
2017). cited by examiner .
Dorrer, C. High-speed measurements for optical telecommunication
systems. IEEE J. Sel. Topics Quantum Electron.12, 843-858 (2006).
cited by applicant .
Li, G. Recent advances in coherent optical communication. Adv. Opt.
Photon. 1, 279-307 (2009). cited by applicant .
Kohler, B., Squier, J., DeLong, K. W., Trebino, R., Yakovlev, V. V.
& Wilson, K. R. Phase and intensity characterization of
femtosecond pulses from a chirped-pulse amplifier by
frequency-resolved optical gating. Opt. Lett. 20, 483-485 (1995).
cited by applicant .
Dorrer, C., De Beauvoir, B., Le Blanc, C., Ranc, S., Rousseau, J.
P., Rousseau, P. & Salin, F. Single-shot real-time
characterization of chirped-pulse amplification systems by spectral
phase interferometry for direct electric-field reconstruction. Opt.
Lett. 24, 1644-1646 (1999). cited by applicant .
Park, Y., Ahn, T. J. & Azana, J. Real-time complex temporal
response measurements of ultrahigh-speed optical modulators. Opt.
Express 17, 1734-1745 (2009). cited by applicant .
Li, B., Zhang, C., Kang, J., Wei, X., Tan, S. & Wong, K. K. 109
MHz optical tomography using temporal magnification. Opt. Lett. 40,
2965-2968 (2015). cited by applicant .
Li, B., Wei, X., Tan, S., Kang, J. & Wong, K. K. Compact and
stable temporally magnified tomography using a phase-locked
broadband source. Opt. Lett. 41, 1562-1565 (2016). cited by
applicant .
Herink, G., Jalali B., Ropers, C. & Solli, D. R. Resolving the
build-up of femtosecond mode-locking with single-shot spectroscopy
at 90 MHz frame rate. Nature Photon. 10, 321-326 (2016). cited by
applicant .
Wei, X., Zhang, C., Li, B. & Wong, K. K. Y. Observing the
spectral dynamics of a mode-locked laser with ultrafast parametric
spectro-temporal analyzer. Paper STh3L.4, CLEO 2015, OSA Technical
Digest (Optical Society of America, 2015), 2 pages. cited by
applicant .
Cundiff, S. T. Soto-Crespo, J. M. & Akhmediev, N. Experimental
evidence for soliton explosions. Phys. Rev. Lett. 88, 073903
(2002). cited by applicant .
Runge, A. F. Broderick, N. G. & Erkintalo, M. Observation of
soliton explosions in a passively mode-locked fiber laser. Optica
2, 36-39 (2015). cited by applicant .
Solli, D. R., Ropers, C., Koonath, P. & Jalali, B. Optical
rogue waves. Nature 450, 1054-1057 (2007). cited by applicant .
Suret, P., El Koussaifi, R., Tikan, A., Evain, C., Randoux, S.,
Szwaj, C. & Bielawski, S. Single-shot observation of optical
rogue waves in integrable turbulence using time microscopy. Nat.
Commun. 7, 13136 (2016). cited by applicant .
Narhi, M., Wetzel, B., Billet, C., Toenger, S., Sylvestre, T.,
Merolla, J. M., Morandotti, R., Dias F., Genty G., Dudley, J. M.
Real-time measurements of spontaneous breathers and rogue wave
events in optical fibre modulation instability. Nat. Commun. 7,
13675. (2016). cited by applicant .
Kolner, B. Space-time duality and the theory of temporal imaging.
IEEE J. Quantum Electron. 30, 1951-1963. (1994). cited by applicant
.
Bennett, C. V. & Kolner, B. H. Principles of parametric
temporal imaging. I. System configurations. J. Quantum Electron.
36, 430-437 (2000). cited by applicant .
Salem, R., Foster, M. A. & Gaeta, A. L. Application of
space-time duality to ultrahigh-speed optical signal processing.
Adv. Opt. Photon. 5, 274-317 (2013). cited by applicant .
Broaddus, D. H., Foster, M. A., Kuzucu, O., Turner-Foster, A. C.,
Koch, K. W., Lipson, M. & Gaeta, A. L. Temporal-imaging system
with simple external-clock triggering. Opt. Express 18, 14262-14269
(2010). cited by applicant .
Foster, M. A., Salem, R., Geraghty, D. F., Turner-Foster, A. C.,
Lipson, M. & Gaeta, A. L. Silicon-chip-based ultrafast optical
oscilloscope. Nature 456, 81-84 (2008). cited by applicant .
Huang, S.-W., Zhou, H., Yang, J., McMillan, J. F., Matsko, A., Yu,
M., Kwong, D.-L., Maleki, L. & Wong, C. W. Mode-locked
ultrashort pulse generation from on-chip normal dispersion
microresonators. Phys. Rev. Lett. 114, 053901 (2015). cited by
applicant .
Huang, S. W., Yang, J., Lim, J., Zhou, H., Yu, M., Kwong, D. L.
& Wong, C. W. A low-phase-noise 18 GHz Kerr frequency microcomb
phase-locked over 65 THz. Sci. Rep. 5, 13355 (2015). cited by
applicant .
Huang, S. W., Yang, J., Yu, M., McGuyer, B. H., Kwong, D. L.,
Zelevinsky, T. & Wong, C. W. A broadband chip-scale optical
frequency synthesizer at 2.7x10-16 relative uncertainty. Sci. Adv.
2, e1501489 (2016). cited by applicant .
Pfeifle, J., Coillet, A., Henriet, R., Saleh, K., Schindler, P.,
Weimann, C., Freude, W., Balakireva, I. V., Larger, L., Koos, C.
& Chembo, Y. K. Optimally coherent Kerr combs generated with
crystalline whispering gallery mode resonators for ultrahigh
capacity fiber communications. Phys. Rev. Lett. 114, 093902 (2015).
cited by applicant .
Lamont, M. R., Okawachi, Y. & Gaeta, A. L. Route to stabilized
ultrabroadband microresonator-based frequency combs. Opt. Lett. 38,
3478-3481 (2013). cited by applicant .
Zhou, H., Huang, S. W., Dong, Y., Liao, M., Qiu, K. & Wong, C.
W. Stability and intrinsic fluctuations of dissipative cavity
solitons in Kerr frequency microcombs. IEEE Photon. J. 7, 1-13
(2015). cited by applicant .
Turitsyna, E. G. et al. The laminar-turbulent transition in a fiber
laser. Nat. Photon. 7, 783-786. (2013). cited by applicant .
Turitsyna, E. G., Falkovich, G. E., Mezentsev, V. K. &
Turitsyn, S. K. Optical turbulence and spectral condensate in
long-fiber lasers. Phys. Rev. A 80, 031804R (2009). cited by
applicant .
Walmsley, I. A. & Dorrer, C. Characterization of ultrashort
electromagnetic pulses. Adv. Opt. Photon. 1, 308-437 (2009). cited
by applicant .
Kane, D. J. & Trebino, R. Single-shot measurement of the
intensity and phase of an arbitrary ultrashort pulse by using
frequency-resolved optical gating. Opt. Lett. 18, 823-825 (1993).
cited by applicant .
Fontaine, N. K., Scott, R. P., Zhou, L., Soares, F. M., Heritage,
J. P. & Yoo, S. J. B.Real-time full-field arbitrary optical
waveform measurement. Nature Photon. 4, 248-254 (2010). cited by
applicant .
Asghari, M. H., Park, Y. & Azana, J. Complex-field measurement
of ultrafast dynamic optical waveforms based on real-time spectral
interferometry. Opt. Express 18, 16526-16538 (2010). cited by
applicant.
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Primary Examiner: Decenzo; Shawn
Attorney, Agent or Firm: Leason Ellis LLP
Claims
We claim:
1. A single-shot optical waveform measurement apparatus that
achieves scalable record length and sub-picosecond resolution
simultaneously for ultrafast non-repetitive waveform
characterization comprises: a fiber-loop based optical buffer that
receives a signal under test, said buffer creating multiple
identical replicas of the signal under test with a pre-defined
period of T.sub.1; a time magnifier integrated with the buffer to
realize temporal scanning using stroboscopic signal acquisition
with a constant time interval, said magnifier measuring the
replicas with a certain time period of T.sub.2; and clock and sync
electronics that synchronize the buffer and magnifier such that if
the measurement period of the time magnifier is T.sub.2, then in
each frame, the time magnifier captures a different section of the
long waveform of the signal under test with a step size equal to
|T.sub.1-T.sub.2| in order to provide a magnified waveform
corresponding to different sections of the signal under test.
2. The optical waveform measurement apparatus of claim 1 further
including a real time recorder of the magnified waveform and a data
processor that stitch together neighboring frames of the magnified
waveform in order to reconstruct a magnified panoramic image of the
original signal under test.
3. The optical waveform measurement apparatus of claim 2 wherein an
effective single-shot recording length is scaled by the number of
replicas without sacrificing the temporal resolution, thus
substantially enhancing a time-bandwidth product (TBWP) of the
apparatus.
4. The optical waveform measurement apparatus of claim 1 wherein
the time magnifier comprises: a first dispersion compensating fiber
(DCF) and large effective area fiber (LEAF) combination for
dispersing the signal from the optical buffer; a mode-locked laser;
a second dispersion compensating fiber (DCF) and large effective
area fiber (LEAF) combination for dispersing the output of the
laser; a wavelength-division multiplexer (WDM) that combines the
output of the first DCF/LEAF combination and the pump (output of
high power EDFA); a highly-nonlinear fiber (HNLF) that receives the
output of the WDM to generate an idler; a first band-pass filter
(BPF) that receives the idler output of the HNLF and limits it to a
certain spectral component; an output dispersion fiber (DCF) that
passes the output of the first BPF; a first low-noise Erbium-doped
fiber amplifier (EDFA) that receives and amplifies the output of
the DCF to form the output of the time magnifier.
5. The optical waveform measurement apparatus of claim 4 wherein
the pump further includes: a second low-noise Erbium-doped fiber
amplifier (EDFA) for receiving the output of the second DCF/LEAF
combination and pre-amplifying it; a second band-pass filter (BPF)
for filtering the output of the second EDFA; a polarization
controller (PC) for controlling the polarization of the output of
the second BPF; and a high-power Erbium-doped fiber amplifier
(EDFA) that amplifies the output of the polarization controller to
produce the pump.
6. The optical waveform measurement apparatus of claim 4 wherein
the first dispersion compensating fiber (DCF) and large effective
area fiber (LEAF) that form the combination are combined according
to the ratio of their dispersion slope so as to provide linear net
dispersion.
7. The optical waveform measurement apparatus of claim 5 wherein
the second BPF selects the spectral component from 1555 nm to 1565
nm.
8. The optical waveform measurement apparatus of claim 1 wherein
the fiber-loop optical buffer comprises: an amplitude modulator
(AM1) for receiving a section of waveform of the signal under test;
a polarization controller for buffering the output of AM1; a 50/50
coupler for coupling the output of polarization controller into a
fiber loop such that one replica of the signal under test is
generated for each cavity round trip of the signal in the loop,
said coupler further coupling out 50% of the buffered waveform as a
replica of the signal in the loop to an output of the buffer, while
the other 50% is circulated for the next round.
9. The optical waveform measurement apparatus of claim 8 wherein
the fiber loop comprises: an optical delay line after the coupler
for fine tuning the cavity period of the loop to match a frame rate
of the time magnifier; a second amplitude modulator (AM2) located
after the delay line which functions as a switch by controlling the
intra-cavity loss, said second amplitude modulator is turned on
only when the signal in the loop passes it, such that it controls
the number of replicas generated from the buffer; a
wavelength-division multiplexer (WDM) with a particular passband
receives the signal from the second amplitude modulator and
minimizes the buffering noise; and an erbium-doped fiber (EDF)
receives and amplifies the signal in the loop; and a laser pumps
the EDF so as to provide a maximum gain to compensate for the total
cavity loss.
10. The optical waveform measurement apparatus of claim 9 wherein
the fiber loop further includes a bandpass filter and polarization
controller in series between the second amplitude modulator and the
WDM.
11. The optical waveform measurement apparatus of claim 1 wherein
the clock and sync electronics comprise: a
repetition-rate-stabilized femtosecond fiber (MLL); a photodetector
which with the MLL generates an electrical clock signal that serves
as the time base of the whole system; an arbitrary waveform
generator (AWG), a delay generator (DG) which with the AWG create
electrical patterns that control the stroboscopic acquisition based
on the clock signal; and three amplitude modulators (AM1, AM2, AM3)
that convert the electrical patterns to the optical domain so as to
control (a) the input signal under test loading (AM1),
optical-buffer switching (AM2) and time-magnifier-pump generation
(AM3), respectively, wherein after the signal under test is loaded
into the buffer, AM2 will be switched on only when the SUT arrives
in each circulation to generate replicas; and wherein AM3 performs
pulse-picking on the MLL to generate a pump for the time magnifier.
Description
TECHNICAL FIELD
The present invention is generally directed to temporal imaging,
and more particularly to the panoramic reconstruction of temporal
images.
BACKGROUND OF THE INVENTION
The ability to characterize arbitrary and non-repetitive optical
waveforms with sub-picosecond (sub-ps) resolution in single-shot
and in real-time is beneficial in different fields, such as
advanced optical communication [1, 2], ultrashort pulses generation
[3, 4], optical devices evaluation [5] and ultrafast bio-imaging
[6, 7]. The references identified in square brackets are listed
below and are incorporated herein by reference in their
entirety.
More importantly, it has helped reveal fascinating ultrafast
phenomena in optics, such as the onset of mode-locking [8, 9],
soliton explosions [10-11] and optical rogue waves [12-14. Temporal
imaging system is one of the most promising techniques perceived
and developed to meet the needs of single-shot, real-time waveform
characterization [15-17]. Based on space-time duality [15-17],
quadratic phase modulation (time-lens) and dispersion can be
properly combined to significantly increase the time-domain
detection bandwidth. On the other hand, just like there are always
limitations on the field-of-view in any spatial imaging system, the
single-shot record length .DELTA.T or the temporal aperture of
temporal imaging systems has previously been limited to less than
300 ps [18].
Owing to this limitation, the time-bandwidth product ("TBWP"),
ratio between the maximum record length .DELTA.T and temporal
resolution .delta.t of state-of-the-art temporal imaging systems
[19] has not exceeded 450. Such a situation hinders the
applications of temporal imaging systems to the study of many
important optical nonlinear dynamic phenomena, where not only fine
temporal details but also long evolution information are necessary
for a comprehensive understanding of the phenomena. For example,
studying the dynamics of dissipative Kerr solitons in
microresonators [20] is of particular interest because of its
potential applications in low-phase noise photonic oscillators
[21], broadband optical frequency synthesizers [22], and coherent
terabit communications [23]. While the soliton generation benefits
greatly from the ultrahigh quality factor (Q) of the
microresonator, the ultrahigh Q also renders its formation and
transition dynamics slowly evolved at a time scale much longer than
the cavity roundtrip time [24, 25], which causes significant
challenges in the experimental real-time observation.
Similarly, an optical metrology system that combines the feats of
fine temporal resolution and long measurement window is also
desired in the study of optical turbulence and laminar-turbulent
transition in fiber lasers [26, 27], which leads to a better
understanding of coherence breakdown in lasers and laser operation
in far-from-equilibrium regimes. To capture comprehensive portraits
of these processes, a temporal imaging system with a TBWP much
greater than 1,000 is necessary.
Meanwhile, limitations on TBWP also exist for other techniques that
achieve comparable performance [28-32]. Single-shot real-time
spectral interferometry [32] has been adopted to reconstruct the
time-domain information, achieving a temporal resolution (.delta.t)
of 400 fs. However, its temporal record length is limited by the
spectral resolution (10 pm) to around 350 ps, which results in a
TBWP of 875.
Another measurement technique combines spectral slicing of the
optical signal with parallel optical homodyne detection using a
frequency comb as a reference [31]. Even though a TBWP larger than
320,000 has been demonstrated at a 160-GHz detection bandwidth, it
is practically challenging to scale the detection bandwidth beyond
1 THz (i.e., sub-ps temporal resolution). Acknowledging current
existing methods, a waveform measurement technique achieving sub-ps
temporal resolution and a scalable record length simultaneously is
urgently needed and it would be a powerful tool for studying
ultrafast dynamics in different areas.
SUMMARY OF THE INVENTION
The present invention is directed to an ultrafast single-shot
waveform characterization system and approach that enable scalable
temporal record-length and sub-ps temporal resolution
simultaneously, thus breaking through the limitation of
time-bandwidth product ("TBWP") in traditional single-shot waveform
measurement techniques.
In order to achieve this goal, a panoramic-reconstruction temporal
imaging ("PARTI") system is proposed. It is analogous to the wisdom
of stitching together multiple mosaic images to achieve a larger
field-of-view (panorama) in the spatial domain. The advantages of
the PARTI system include: 1) Compared to existing techniques that
can achieve sub-ps temporal resolution, the technique of the
present invention achieves orders of magnitude longer record length
(tens of nanosecond) in a single shot manner. 2) The generalized
idea of waveform replication combined with single-shot acquisition
is also applicable to other measuring techniques, such as real-time
spectral interferometry [32]. Therefore, the technique of the
present invention not only represents an advanced temporal imaging
system, but also stimulates more analogous innovations in a family
of single-shot ultrafast measurement techniques.
The optical buffer in the PARTI system creates multiple identical
replicas of the signal under test ("SUT") with a constant time
interval, which is subsequently measured by the following time
magnifier, thus realizing the temporal scanning on a transient SUT.
Using the optical buffer, SUT replicas can be generated with a
pre-defined period of T.sub.1. If the measurement period of the
time magnifier is T.sub.2, then in each frame, the time magnifier
captures a different section of the long waveform with a step size
equal to |T.sub.1-T.sub.2|.
The output of the PARTI system represents the magnified waveform
corresponding to different sections of the long SUT and is recorded
by a high-speed real-time oscilloscope. After data processing,
neighboring frames of magnified waveform are stitched together to
reconstruct a magnified panoramic image of the original SUT.
Therefore, the effective single-shot recording length is scaled by
the number of replicas without sacrificing the temporal resolution,
thus substantially enhancing the TBWP.
In an exemplary embodiment the apparatus for carrying out the
invention includes a fiber-loop based optical buffer that receives
a signal under test. The buffer creates multiple identical replicas
of the signal under test with a pre-defined period of T.sub.1. A
time magnifier integrated with the buffer causes temporal scanning
using stroboscopic signal acquisition with a constant time
interval. The magnifier measures the replicas with a certain time
period of T.sub.2 and clock and sync electronics synchronize the
buffer and magnifier such that if the measurement period of the
time magnifier is T.sub.2, then in each frame the time magnifier
captures a different section of the long waveform of the signal
under test with a step size equal to |T.sub.1-T.sub.2|. This
provides a magnified waveform corresponding to different sections
of the signal under test.
BRIEF DESCRIPTION OF THE DRAWINGS
The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
The foregoing and other objects and advantages of the present
invention will become more apparent upon reference to the following
detailed description and annexed drawings in which like
designations denote like elements in the various views, and
wherein:
FIG. 1 is a schematic diagram of a PARTI system according to the
present invention illustrating the principles of operation;
FIG. 2 is a set-up of the low-aberration time magnifier of the
system of FIG. 1;
FIG. 3 is a set-up of the high-fidelity optical buffer of the
system of FIG. 1;
FIGS. 4A and 4B illustrate the synchronization scheme between the
optical buffer and the time magnifier of the system of FIG. 1,
wherein FIG. 4A illustrates an apparatus set-up and FIG. 4B is an
operational timing chart illustrating the realization of
synchronization;
FIGS. 5A and 5B illustrate an exemplary result of applying the
PARTI system to the study of dissipative Kerr soliton dynamics in a
microresonator, wherein FIG. 5A illustrates a soliton evolution
process where a triplet soliton state evolves into a singlet
soliton state through soliton colliding and FIG. 5B illustrates a
different evolution process which starts with a doublet soliton
state, has a triplet soliton state in the middle and ends up with a
singlet soliton state; and
FIG. 6 illustrates the present invention in a passive buffering
scheme.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows how the PARTI system overcomes the limitation of TBWP
in conventional temporal imaging systems and thus captures
slowly-evolved soliton dynamics. The signal under test (SUT) 10 is
an exemplary pulse train. Since the SUT is transient and
non-repetitive, the concept of image stitching in the spatial
domain cannot be conveniently adopted in temporal imaging systems.
To address this problem, a fiber-loop based optical buffer 12 is
integrated with a time magnifier 14 to realize temporal scanning
using stroboscopic signal acquisition, a technique commonly adopted
in sampling oscilloscopes. As shown in FIG. 1, the optical buffer
12 in the PARTI system creates multiple identical replicas of the
signal under test with a constant time interval. These replicas
will be subsequently measured by the time magnifier 14 that follows
the buffer. Thus the temporal scanning on a transient SUT is
realized.
Using the optical buffer 12, the SUT replicas can be generated with
a pre-defined period of T.sub.1 as shown in FIG. 1. If the
measurement period of the time magnifier 14 is T.sub.2, then in
each frame, the time magnifier captures a different section of the
long waveform with a step size equal to |T.sub.1-T.sub.2|. The
buffer and time magnifier are synchronized by sync electronics 13
driven by clock 15. The output of the PARTI system represents the
magnified waveform corresponding to different sections of the long
SUT and is recorded by a high-speed real-time oscilloscope 16.
After data processing in computer system 18, neighboring frames of
magnified waveform are stitched together to reconstruct a magnified
panoramic image 19 of the original SUT. Therefore, the effective
single-shot recording length is scaled by the number of replicas
without sacrificing the temporal resolution, thus substantially
enhancing the TBWP.
The foundation of the PARTI system is the parametric time magnifier
14 with low aberration. An exemplary embodiment of the time
magnifier is shown in FIG. 2. The parametric time lens is
implemented through a four-wave mixing (FWM) process in a 50-m
highly-nonlinear fiber (HNLF). The FWM process was chosen, as
opposed to other parametric processes, because it allows
high-quality processing of SUT, pump and output simultaneously in
the telecommunication band. In addition, since multiple frames of
magnified waveform need to be stitched together to obtain the
panoramic image, it is critical to ensure a stable impulse response
across the recording window of the time magnifier, i.e. a
low-aberration FWM time magnifier. For an in-focus time magnifier,
the main aberration comes from the third order dispersion ("TOD")
in the dispersive path for input and pump. In order to construct a
low-aberration time magnifier, i.e., to minimize the
third-order-dispersion-induced aberration, with a long recording
length, both the input and the pump dispersions are provided by
proper combination of dispersion compensating fiber (DCF) and large
effective-area fiber (LEAF). This combination achieves large linear
dispersion (fourth and higher order dispersion neglected).
As shown in FIG. 2, both the input dispersion 24 and the pump
dispersion 24' are provided by combining DCF and LEAF in devices
24, 24'. Since the LEAF has the opposite dispersion slope [0.08
psnm.sup.-2km.sup.-1] compared to the DCF [-0.598
psnm.sup.-2km.sup.-1], combining the two types of fiber according
to the ratio of their dispersion slope results in linear net
dispersion. Moreover, LEAF features in very small
dispersion-to-dispersion-slope ratio (K.sub.LEAF=D/S=45 nm)
compared to standard single-mode fiber (SMF) (K.sub.SMF=D/S=275
nm). Therefore, using a LEAF fiber to compensate the dispersion
slope of the DCF sacrifices much less net dispersion compared with
using SMF, which facilitates achieving large linear dispersion with
moderate insertion loss.
In the system shown in FIG. 2, the input SUT is dispersed for 35
ps.sup.2 in device 24 before being combined with the pump through
the wavelength-division multiplexer (WDM) 26. In the lower branch
of the system, the output of the MLL goes through a dispersion of
71.2 ps.sup.2 in device 24' and is then pre-amplified by a
low-noise Erbium-doped fiber amplifier ("EDFA") 23. The output of
amplifier 23 goes through band-pass filter ("BPF") 25, which
selects the spectral component from 1555 nm to 1565 nm. The filter
output is passed through polarization controller ("PC") 27 and is
subsequently amplified again to 100 mW in EDFA 29 to generate the
pump for the time magnifier. The pump and SUT are launched together
into the highly-nonlinear fiber (HNLF) 28, and the generated idler
is filtered out in BPF 30. The output of filter 30 is passed
through the output dispersion DCF 32 (2152.5 ps.sup.2) and its
output is then amplified again in EDFA 34 to become the final
output 33 of the time magnifier.
Overall, the system satisfies the imaging condition
.PHI.''.PHI.''.PHI.'' ##EQU00001##
where the .PHI.''.sub.1 (35 ps.sup.2), .PHI.''.sub.2 (2152.5
ps.sup.2), and .PHI.''.sub.f (-35.6 ps.sup.2) are the input,
output, and focal group-delay dispersions, respectively, while the
minus sign originates from the phase conjugation during the chosen
parametric process. Therefore, the temporal magnification ratio
is
.PHI.''.PHI.'' ##EQU00002##
In order to generate multiple replicas of SUT for temporal
scanning, a fiber-loop based optical buffer is needed as shown in
FIG. 3. The buffer generates multiple high fidelity replicas of
arbitrary signals under test with a fine-tunable period for
subsequent stroboscopic signal acquisition. A SUT is loaded through
amplitude modulator ("AM") 35 and polarization controller 37 into
the buffer through the 50/50 coupler 39. One replica will be
generated when the SUT is circulated for each cavity round
trip.
During operation, a section of waveform will be carved out by
amplitude modulator 35 (AM1) and loaded into the buffer through the
50/50 coupler 39. After each circulation inside the fiber-loop
cavity, 50% of the buffered waveform is coupled out through output
36 as a replica, while the other 50% is circulated for the next
round. In the configuration of FIG. 3, the total cavity length is
designed to be around 8.2 m and the cavity period can be fine-tuned
from 39.7 ns to 40 ns using the optical delay-line 40 in order to
match the frame rate of the time magnifier. Amplitude modulator 42
(AM2) functions as a switch by controlling the intra-cavity loss.
The switch is turned on only when the SUT passes AM2 and therefore,
AM2 controls the number of replicas generated from the buffer 12.
More importantly, the periodic switching of AM2 prevents the
self-lasing operation of the optical buffer, which substantially
suppresses the amplification noise during the buffering.
Additionally, a WDM filter 48 with a passband from 1537 nm to 1547
nm further minimizes the buffering noise. A 980-nm laser diode 46
pumping a 2-m erbium-doped fiber (EDF) 50 through WDM 48 provides a
maximum gain of around 20 dB to compensate the total cavity loss
(.apprxeq.12 dB). To minimize the dispersion distortion, 0.5-m DCF
is added to the cavity. Therefore, the influence of residual net
dispersion is small enough to be neglected. Finally, by optimizing
the polarization controllers (PC) 37, 45 both outside and inside
the cavity, the buffer generates high-fidelity replicas of the
input waveform.
The details of the synchronization of the optical buffer and the
time magnifier are shown in FIGS. 4A and 4B. In order to emphasize
the key components for synchronization, the optical buffer and the
time magnifier are shown simplified in the schematic of FIG. 4A.
The key electronics can be divided into the following three groups.
First of all, a repetition-rate-stabilized femtosecond fiber MLL 52
and a 1.2-GHz photodetector 53 together generate a 250-MHz
electrical clock signal, which serves as the time base of the whole
system. Secondly, an arbitrary waveform generator (AWG) 54, and a
delay generator (DG) 56 create electrical patterns that control the
stroboscopic acquisition based on the clock signal. Finally, the
three amplitude modulators (AM1, AM2, AM3) convert the electrical
patterns to the optical domain, so as to control the input SUT
loading (AM1) 57, optical-buffer switching (AM2) 58 and
time-magnifier-pump generation (AM3) 59, respectively.
The detailed timing chart of the system is shown in FIG. 4B. The
driving patterns for AM1, AM2 and AM3 as well as the generated
replicas are shown schematically. The corresponding pulse width and
periods are also labelled in the figure. The vertical black dashed
line separates the two consecutive frames.
As indicated by the vertical black dashed line, the whole system is
operated with a frame rate of 2 MHz as an example. In every 500 ns,
AM1 will load from the input a 5-ns-long waveform as the signal
under test SUT (first horizontal axis). After the SUT is loaded
into the buffer, AM2 will be switched on only when the SUT arrives
in each circulation. Therefore, in the second horizontal axis, AM2
opens every 40 ns and generates ten identical replicas in each
500-ns frame. Ideally, the separation between each gating is
identical to the cavity period of the buffer (39.85 ns). However,
being limited by the sampling speed of AWG (1 Gss.sup.-1), the
separation is set as 40 ns. Nevertheless, since each SUT is only
circulated 10 times inside the buffer and the gating width (10 ns)
is much broader than the SUT duration, the slight mismatch between
the gating period and the cavity period will not influence the
performance of the buffer.
After the buffering, ten replicas will be generated with a
separation equal to the cavity period (fourth horizontal axis). AM3
performs pulse-picking on the MLL to generate a pump for the time
magnifier every 40 ns (third horizontal axis). Owing to the period
difference (150 ps) between the time magnifier and the SUT
replicas, the time magnifier will scan the SUT from left to right
with a step of 150 ps, thus realizing the temporal scanning on a
long SUT.
Finally, to demonstrate the capabilities of the PARTI system, the
system is applied to observe the dynamic evolution of dissipative
Kerr solitons inside an ultrahigh-Q microresonator. The final
output of the system is detected by an 18-GHz photodetector and
then digitized and recorded by a real-time oscilloscope. After data
processing on the measurement results, two sections of 1.5-ns-long
waveform with a 740-fs resolution are reconstructed, which
represent a TBWP of more than 2000. With the unprecedented
measurement capability, fascinating dissipative Kerr soliton
dynamics in a high-Q microresonator is observed. To clearly
visualize the evolution details, a one-dimensional waveform is
sectioned according to the cavity roundtrip time (11.29 ps) of the
microresonator to rearrange the data into a two-dimensional matrix
and create 2D evolution portraits to depict the dissipative Kerr
soliton transition dynamics.
In the first case, as shown in FIG. 5A, at the beginning stage (0
ps to around 400 ps); three solitons (triplet state) with almost
equal intensity exist in the cavity. After that, in the middle
stage (400 ps to around 800 ps), the first two solitons starts to
be attracted to each other and eventually merge into a singlet
soliton at around 800 ps. The third soliton is shifted upwards
during the merging of the other two solitons. However, the third
soliton does not survive during the transition and starts to fade
after 500 ps. After this transitioning middle stage, a singlet
soliton state is achieved inside the cavity, and the state remains
for more than 600 ps, or 53 cavity roundtrips. Black dashed curves
emphasizing the soliton transition traces are plotted against the
2D portrait, which is obtained by polynomial fitting the peak
positions of the solitons.
In addition to the first example, a different dynamic process is
also observed which also generates the singlet soliton state
eventually but without soliton fusion. As shown in FIG. 5B, in the
first stage (0 to around 370 ps) two solitons co-exist in the
cavity. In the meantime, the doublet solitons repulse each other
slightly and the first soliton gradually fades away. At around 370
ps, the upper soliton disappears, but at the same time two other
solitons emerge. In the second stage (370 ps to 1 ns), in contrast
to the first stage, the triplet solitons are attracted to the
center slowly. At the end of the second stage, both the top and
bottom solitons fade away, while the middle one survives and
evolves into a singlet soliton with higher intensity in the final
stage (1 ns to 1.5 ns). Similar to the first example, the singlet
soliton state is much more stable compared to previous states and
lasts over 500 ns.
In addition, the PARTI system can also be realized in a passive
buffering scheme as shown in FIG. 6. FIG. 6 illustrates a set-up of
the optical buffer with eight 50/50 couplers 60 cascaded together
to generate 128 replicas from the original SUT with a minimum
attenuation of around 21 dB (7.times.3 dB) on the intensity of each
replica. Dispersion-shifted fiber (DSF) sections 61 with precise
lengths of L, 2L, 4L, . . . are inserted between each coupling
stages to induce required delay among replicas. Under such an
approach, the attenuation can be compensated by just one stage of
amplifier before launching into the temporal imaging system. In
particular, a single stage of amplification using an erbium-doped
fiber amplifier ("EDFA") 62 can be placed at the final output port
to compensate the attenuation of the signals. This will
significantly reduce the noise-induced distortion and therefore
greatly extend the potential scalability of the PARTI system. The
optical delay in each stage of 50/50 coupler 60 is precisely
controlled by dispersion shifted fiber (DSF) 61 and tunable optical
delay line 63. Since DSF has almost zero dispersion at 1.5 .mu.m,
the main contribution to dispersion comes from the pigtails of the
50/50 couplers, which are made of single-mode fiber ("SMF").
Therefore, the dispersion experienced by each replica is the same
and thus can be compensated together by a spool of DCF 64 to
eliminate the dispersive distortion.
Since there is no tuning part, once the period of replication is
fixed, such a passive scheme significantly reduces the complexity
of synchronization between the buffer and the time magnifier, which
makes the PARTI system more user-friendly. This alternative
embodiment is mostly preferred in circumstances where the PARTI
system is applied for the study of a specific phenomenon so that
the buffering period can be customized according to the
requirement.
REFERENCES
The references listed below are cited throughout the specification
and are identified by the corresponding number(s) placed in square
brackets [ ]. Each of the following references is incorporated
herein by reference in its entirety: 1. Dorrer, C. High-speed
measurements for optical telecommunication systems. IEEE J. Sel.
Topics Quantum Electron. 12, 843-858 (2006). 2. Li, G. Recent
advances in coherent optical communication. Adv. Opt. Photon. 1,
279-307 (2009). 3. Kohler, B., Squier, J., DeLong, K. W., Trebino,
R., Yakovlev, V. V. & Wilson, K. R. Phase and intensity
characterization of femtosecond pulses from a chirped-pulse
amplifier by frequency-resolved optical gating. Opt. Lett. 20,
483-485 (1995). 4. Dorrer, C., De Beauvoir, B., Le Blanc, C., Ranc,
S., Rousseau, J. P., Rousseau, P. & Salin, F. Single-shot
real-time characterization of chirped-pulse amplification systems
by spectral phase interferometry for direct electric-field
reconstruction. Opt. Lett. 24, 1644-1646 (1999). 5. Park, Y., Ahn,
T. J. & Azana, J. Real-time complex temporal response
measurements of ultrahigh-speed optical modulators. Opt. Express
17, 1734-1745 (2009). 6. Li, B., Zhang, C., Kang, J., Wei, X., Tan,
S. & Wong, K. K. 109 MHz optical tomography using temporal
magnification. Opt. Lett. 40, 2965-2968 (2015). 7. Li, B., Wei, X.,
Tan, S., Kang, J. & Wong, K. K. Compact and stable temporally
magnified tomography using a phase-locked broadband source. Opt.
Lett. 41, 1562-1565 (2016). 8. Herink, G., Jalali B., Ropers, C.
& Solli, D. R. Resolving the build-up of femtosecond
mode-locking with single-shot spectroscopy at 90 MHz frame rate.
Nature Photon. 10, 321-326 (2016). 9. Wei, X., Zhang, C., Li, B.
& Wong, K. K. Y. Observing the spectral dynamics of a
mode-locked laser with ultrafast parametric spectro-temporal
analyzer. Paper STh3L.4, CLEO 2015, OSA Technical Digest (Optical
Society of America, 2015). 10. Cundiff, S. T. Soto-Crespo, J. M.
& Akhmediev, N. Experimental evidence for soliton explosions.
Phys. Rev. Lett. 88, 073903 (2002). 11. Runge, A. F. Broderick, N.
G. & Erkintalo, M. Observation of soliton explosions in a
passively mode-locked fiber laser. Optica 2, 36-39 (2015). 12.
Solli, D. R., Ropers, C., Koonath, P. & Jalali, B. Optical
rogue waves. Nature 450, 1054-1057 (2007). 13. Suret, P., El
Koussaifi, R., Tikan, A., Evain, C., Randoux, S., Szwaj, C. &
Bielawski, S. Single-shot observation of optical rogue waves in
integrable turbulence using time microscopy. Nat. Commun. 7, 13136
(2016). 14. Nirhi, M., Wetzel, B., Billet, C., Toenger, S.,
Sylvestre, T., Merolla, J. M., Morandotti, R., Dias F., Genty G.,
Dudley, J. M. Real-time measurements of spontaneous breathers and
rogue wave events in optical fibre modulation instability. Nat.
Commun. 7, 13675. (2016). 15. Kolner, B. Space-time duality and the
theory of temporal imaging. IEEE J. Quantum Electron. 30,
1951-1963. (1994). 16. Bennett, C. V. & Kolner, B. H.
Principles of parametric temporal imaging. I. System
configurations. J. Quantum Electron. 36, 430-437 (2000). 17. Salem,
R., Foster, M. A. & Gaeta, A. L. Application of space-time
duality to ultrahigh-speed optical signal processing. Adv. Opt.
Photon. 5, 274-317 (2013). 18. Broaddus, D. H., Foster, M. A.,
Kuzucu, O., Turner-Foster, A. C., Koch, K. W., Lipson, M. &
Gaeta, A. L. Temporal-imaging system with simple external-clock
triggering. Opt. Express 18, 14262-14269 (2010). 19. Foster, M. A.,
Salem, R., Geraghty, D. F., Turner-Foster, A. C., Lipson, M. &
Gaeta, A. L. Silicon-chip-based ultrafast optical oscilloscope.
Nature 456, 81-84 (2008). 20. Huang, S.-W., Zhou, H., Yang, J.,
McMillan, J. F., Matsko, A., Yu, M., Kwong, D.-L., Maleki, L. &
Wong, C. W. Mode-locked ultrashort pulse generation from on-chip
normal dispersion microresonators. Phys. Rev. Lett. 114, 053901
(2015). 21. Huang, S. W., Yang, J., Lim, J., Zhou, H., Yu, M.,
Kwong, D. L. & Wong, C. W. A low-phase-noise 18 GHz Kerr
frequency microcomb phase-locked over 65 THz. Sci. Rep. 5, 13355
(2015). 22. Huang, S. W., Yang, J., Yu, M., McGuyer, B. H., Kwong,
D. L., Zelevinsky, T. & Wong, C. W. A broadband chip-scale
optical frequency synthesizer at 2.7.times.10-16 relative
uncertainty. Sci. Adv. 2, e1501489 (2016). 23. Pfeifle, J.,
Coillet, A., Henriet, R., Saleh, K., Schindler, P., Weimann, C.,
Freude, W., Balakireva, I. V., Larger, L., Koos, C. & Chembo,
Y. K. Optimally coherent Kerr combs generated with crystalline
whispering gallery mode resonators for ultrahigh capacity fiber
communications. Phys. Rev. Lett. 114, 093902 (2015). 24. Lamont, M.
R., Okawachi, Y. & Gaeta, A. L. Route to stabilized
ultrabroadband microresonator-based frequency combs. Opt. Lett. 38,
3478-3481 (2013). 25. Zhou, H., Huang, S. W., Dong, Y., Liao, M.,
Qiu, K. & Wong, C. W. Stability and intrinsic fluctuations of
dissipative cavity solitons in Kerr frequency microcombs. IEEE
Photon. J. 7, 1-13 (2015). 26. Turitsyna, E. G. et al. The
laminar-turbulent transition in a fiber laser. Nat. Photon. 7,
783-786. (2013). 27. Turitsyna, E. G., Falkovich, G. E., Mezentsev,
V. K. & Turitsyn, S. K. Optical turbulence and spectral
condensate in long-fiber lasers. Phys. Rev. A 80, 031804R (2009).
28. Walmsley, I. A. & Dorrer, C. Characterization of ultrashort
electromagnetic pulses. Adv. Opt. Photon. 1, 308-437 (2009). 29.
Kane, D. J. & Trebino, R. Single-shot measurement of the
intensity and phase of an arbitrary ultrashort pulse by using
frequency-resolved optical gating. Opt. Lett. 18, 823-825 (1993).
30. Dorrer, C., De Beauvoir, B., Le Blanc, C., Ranc, S., Rousseau,
J. P., Rousseau, P. & Salin, F. Single-shot real-time
characterization of chirped-pulse amplification systems by spectral
phase interferometry for direct electric-field reconstruction. Opt.
Lett. 24, 1644-1646 (1999). 31. Fontaine, N. K., Scott, R. P.,
Zhou, L., Soares, F. M., Heritage, J. P. & Yoo, S. J.
B.Real-time full-field arbitrary optical waveform measurement.
Nature Photon. 4, 248-254 (2010). 32. Asghari, M. H., Park, Y.
& Azafia, J. Complex-field measurement of ultrafast dynamic
optical waveforms based on real-time spectral interferometry. Opt.
Express 18, 16526-16538 (2010).
Specific features of the invention are shown in one or more of the
drawings for convenience only, as each feature may be combined with
other features in accordance with the invention. Alternative
embodiments will be recognized by those skilled in the art and are
intended to be included within the scope of the claims.
Accordingly, the above description should be construed as
illustrating and not limiting the scope of the invention. All such
obvious changes and modifications are within the patented scope of
the appended claims.
* * * * *